Solvent effects on rechargeable lithium cells

Abstract

The behaviour of several solvents in rechargeable lithium cells employing two different structure type cathodes, ns-V 6O 13 a framework oxide, and TiS 2 a layered material, was compared. Excellent cycling behaviour and high energy were obtained for the Li/ns-V 6O 13 cell at current densities as high as 5 mA cm −2 in the temperature range 25 to −40 °C. Cells utilizing an electrolyte of 2 M LiAsF 6 in methyl formate were discharged at a current density of 2 mA cm −2 at −40 °C with 37% cell efficiency at an energy density of 255 W h kg −1 (based on active material). Use of an LiAsF 6/2-MeTHF electrolyte with ns-V 6O 13 resulted in satisfactory cycle-life, but at significantly reduced capacities than observed with the LiAsF 6/MF electrolyte. This is attributed to the lower conductivities of 2-MeTHF solutions. The results for Li/TiS 2 cells are in direct contrast with those observed for ns-V 6O 13. Use of MF solutions with TiS 2 results in extremely low capacities while capacities and cycle life in 2-MeTHF solutions are quite good. These differences are attributed to a combination of factors including solvent co-intercalation, ion salvation, and solvent decomposition.